Citrus Tristeza Virus: An Increasing Trend in the Virus Occurrence and Distribution in Citrus Fruits of Northwest, Pakistan

Abstract

Citrus tristeza clostervirus (CTV) is one of the most damaging fruit viruses playing havoc in citrus orchards around the world. Here, we report, an ELISA-based indexing of citrus trees over a period of eight years (2002 to 2010) in Northwest Pakistan, revealing that the incidence of CTV is increasing mainly with the distribution of infected rootstocks, putting citrus industry at the verge of complete annihilation. The surveys revealed that the average incidence of CTV in 10 major citrus growing districts in the Northwest of Pakistan has steadily increased from 24% (in 2002) to 31, 35, 39 and 44 in 2004, 2006, 2008, 2010, respectively. Maximum per cent increase of CTV was in citrus orchards in district Haripur, that is, 27.50% and followed by 26% increase of the virus incidence in district Swat during 2002 to 2010. The incidence of the virus was correlated with use of sour orange as root stock with rough lemon. In orchards, where rough lemon was used as root stock; the incidence of CTV was comparatively low. A comparative study of the virus incidence conducted during 2006 to 2012 in sweet orange trees grafted on sour orange and rough lemon in Northwest indicated an average per cent incidence 43 and 37, respectively. This is the first comprehensive study on citrus fruits to determine an increasing trend of CTV in Northwest of Pakistan where citrus industry has been a major source of income for local farmers. An extensive rescue plan needs to be placed to avoid complete destruction of this exportbased industry.

Keywords: Citrus, Tristeza, Citrus Tristeza Clostervirus (CTV), ELISA, Incidence, Pakistan